1. Field of the Invention
This invention relates generally to a method and an apparatus for operating a tool in a wellbore. More particularly, the invention relates to positioning a tool in a wellbore and setting the tool in a fixed position. Still more particularly, the invention relates to actuation of a downhole hydraulic tool by an actuation apparatus that uses a pressure differential in a conduit carrying a fluid flow to actuate the downhole hydraulic tool.
2. Description of the Related Art
Hydraulically-actuated tools such as packers and anchor assemblies have long been used in the drilling industry. A tool often used in conjunction with anchors or packers is a deflector, which is commonly called a whipstock. A deflector includes an inclined face and is typically used to direct a drill bit or cutter in a direction that deviates from the existing wellbore. The combination deflector and anchor (or packer) is frequently termed a sidetrack system. Sidetrack systems have traditionally been used to mill a window in the well casing, and thereafter to drill through the casing window and form the lateral wellbore.
Originally, such a sidetrack operation required two trips of the drill string. The first trip was used to run and set the anchor or packing device at the appropriate elevation in the wellbore. With the anchor or packer in place, the drill string was then removed from the well and a survey was made to determine the orientation of a key on the upper end of the anchor-packer. With that orientation known, the deflector was then configured on the surface so that when the deflector engaged the anchor-packer in the wellbore, it would be properly oriented. So configured, the deflector, along with an attached cutter, was then lowered in the wellbore on the drill string and secured to the anchor-packer. Once connected to and supported by the packer, the deflector directed the cutter so that a window would be milled in the casing of the wellbore at the desired elevation and in the preselected orientation. This two-trip operation for setting the anchor-packer and then lowering the deflector and cutter is time-consuming and expensive, particularly in very deep wells.
To eliminate the expense associated with two trips of the drill string, an improved sidetrack system was developed which required only a single trip. Such a system includes a deflector having an anchor-packer connected at its lower end, and a cutter assembly at its upper end connected by a shearable connection. Using such a system, the deflector is oriented by first lowering the apparatus into the cased wellbore on a drill string. A wireline survey instrument is then run through the drill string to check for the proper orientation of the suspended deflector. After the deflector is properly oriented in the wellbore, and the anchor-packer set, the drill string is then lowered causing the cutter assembly to become disconnected from the deflector. As the cutter is lowered further, the inclined surface of the deflector urges the rotating cutter against the well casing, causing the cutter to mill a window in the casing at the predetermined orientation and elevation.
To be contrasted with wireline devices, there exist today a variety of systems that are capable of collecting and transmitting data from a position near the drill bit while drilling is in progress. Such measuring-while-drilling (“MWD”) systems are typically housed in a drill collar at the lower end of the drill string. In addition to being used to detect formation data, such as resistivity, porosity, and gamma radiation, all of which are useful to the driller in determining the type of formation that surrounds the wellbore, MWD tools are also useful in surveying applications, such as, in determining the direction and inclination of the drill bit. Present MWD systems typically employ sensors or transducers which, while drilling is in progress, continuously or intermittently gather the desired drilling parameters and formation data and transmit the information to surface detectors by some form of telemetry, most typically a mud pulse system. The mud pulse system creates acoustic signals in the drilling mud that is circulated through the drill string during drilling operations. The information acquired by the MWD sensors is transmitted by suitably timing the formation of pressure pulses in the mud stream. The pressure pulses are received at the surface by pressure transducers that convert the acoustic signals to electrical pulses, which are then decoded by a computer.
MWD tools presently exist that can detect the orientation of the drill string without the difficulties and drawbacks described above that are inherent with the use of wireline sensors. However, known MWD tools typically require drilling fluid flow rates of approximately 250 gallons per minute to start the tool, and 350 to 400 gallons per minute to gather the necessary data and transmit it to the surface via the mud pulse telemetry system. The conventional bypass valves used in present-day sidetrack systems for circulating drilling fluid and transporting a wireline sensor to the deflector tend to close, and thereby actuate the anchor-packer, at flow rates of approximately 100 gallons per minute, or even less. Thus, while it might be desirable to combine MWD sensors in a sidetrack system, if drilling mud was circulated through the drill string at the rate necessary for the MWD tool to detect and communicate to the driller the orientation of the deflector, the bypass valve would close and the anchor-packer would be set prematurely, before the deflector was properly oriented. As described in the following paragraphs, there are several different methods for setting a downhole tool such as an anchor-packer.
An improved apparatus for setting a hydraulically actuated downhole tool in a wellbore is disclosed in Bailey, U.S. Pat. No. 5,443,129, which is incorporated herein by reference in its entirety. The '129 apparatus utilizes a bypass valve located in the run-in string below the MWD device and above the cutter. The valve is in an open position while the MWD device is operating thereby diverting fluid flow and pressure from the tubular to the annulus without creating a pressure sufficient to actuate a downhole tool. Upon completion of operation of the MWD device, the bypass valve is remotely closed. Thereafter, selectively operable ports in the cutter are opened and the tubular therebelow is pressurized to a point necessary to actuate the tool. While the apparatus of the '129 patent allows operation of a MWD device without the inadvertent actuation of a downhole tool, the bypass valve is complex requiring many moving parts and prevents the continuous flow of fluid through the cutter. Additionally, the bypass valve may not function properly in a wellbore that contains little or no fluid. Finally, the fluid borne sediment tends to settle and collect in the cutter.
An apparatus to actuate a downhole tool is disclosed in Brunnert, U.S. Pat. No. 6,364,037, which is incorporated herein by reference in its entirety. The '037 invention provides an apparatus for actuating a downhole tool by utilizing a pressure differential created by fluid flowing through a conduit. The conduit is in communication with a pressure sensing line that is selectively exposed to areas of the conduit having different pressures. By exposing the pressure sensing line to a portion of the conduit having a predetermined pressure therein, the pressure sensing line causes actuation of a hydraulic tool therebelow. While the apparatus of the '037 patent allows operation of a MWD device without the inadvertent actuation of a downhole tool, the apparatus is complex requiring many moving parts.
A whipstock setting apparatus is disclosed in Braddick, U.S. Pat. No. 5,193,620, which is incorporated herein by reference in its entirety. The '620 invention provides a whipstock setting apparatus that includes a whipstock and a mandrel. A downhole tool including a mechanical weight set packer and upper and lower cone and slip means are mounted on the mandrel above and below the downhole tool. The mandrel is releasably connected to the downhole tool to prevent premature longitudinal movement while accommodating the relative longitudinal movement at a predetermined point. The components of the whipstock assembly and downhole tool are secured to maintain alignment with the face of the whipstock while lowering the whipstock in the well tubular member. Thereafter, the mandrel is released and the whipstock is oriented in the well tubular member. Subsequently, the oriented whipstock and downhole tool are mechanically anchored in the well tubular member by longitudinal movement of the work string. While the apparatus of the '620 patent actuates the downhole tool without any complex hydraulic mechanism, the manipulation of the piping string to initiate the sequence of events to set the whip stock setting apparatus may not be effective in a deviated wellbore due to the angle of the wellbore and frictional problems.
A one-trip whipstock milling system is disclosed in Ross, U.S. Pat. No. 5,947,201, which is incorporated herein by reference in its entirety. The '201 invention provides a bottomhole assembly that includes a whipstock milling system, a downhole tool, a whipstock and orientation instrumentation. After the bottomhole assembly is located in the wellbore, the wellbore is pressurized to actuate the downhole tool. Thereafter, the milling operation cuts a window in the surrounding casing. While the apparatus of the '201 patent actuates the downhole tool without a complex hydraulic mechanism or mechanical manipulation of the piping string, the pressurizing of the wellbore is very costly and will not operate properly if there is little or no fluid in the wellbore.
There is a need therefore, for a single trip sidetrack apparatus permitting a continuous flow of well fluid therethrough while allowing the actuation of a hydraulically actuated tool at a predetermined position in the borehole. There is a further need therefore, for a single trip sidetrack apparatus that does not depend on a value to prevent inadvertent actuation of a downhole tool. There is a further need for an actuation apparatus that allows fluid to flow therethrough before and during actuation of a downhole tool. There is yet a further need for actuating a hydraulically actuated tool in a wellbore that contains little or no wellbore fluid. Finally, there is a need for a single trip sidetrack apparatus that contains an actuation apparatus with no moving parts.